Control R package versioning

[lukejharmon]

R package updates can break Arbor functionality. We should maintain strict control over which versions we are loading, and allow someone to approve updates only when we know they work.

[jeffbaumes]

+1. According to

http://stackoverflow.com/questions/17082341/installing-older-version-r-package

the answer is to point to specific source tarballs for each install - seems there is not a simple version argument in install.packages. Looks like the answer to this is to track down all those URLs and change Ansible to use them. We should also do this when testing things in Travis.

Jeff

[lukejharmon]

Another option: http://rstudio.github.io/packrat/

[jeffbaumes]

That looks way better if it works like it seems to say. I imagine @lukejharmon or @uyedaj could perform packrat::snapshot() on a known working Arbor R environment and post the result somewhere as a public URL (full R source packages snapshot), which we then download and install in Ansible. I don't think we want to check that snapshot into Git.